Does running a lightning node require a full node or can you use a pruned node?
Discussion
You can technically run it on a pruned node, but if you run a node for a long time and say you're only keeping something like, I don't know, let's go with a small number, like five gigs worth of transaction data, you will eventually lose where your channel is pinned on the chain.
So in theory I could run a node that starts at the block height when my channel was opened & saves from then on?
Yes, but pruned nodes don't work that way unless there's some options I'm unaware of. (I'm actually unsure if you can pick a starting block height, for instance.) No matter what your number was for saving however many gigs worth of blocks, you would eventually hit that limit and prune out your old blocks to make space for new ones.
Interesting thank you
Nah. The node prunes the block data but maintains an index of transactions.